Both of the parents of 'Gentle Giant' have 'George Hardy' as an ancestor.

In the case of the tetraploid 'Gentle Giant', a tetraploid crossed with a triploid produced a tetraploid indicating that reduced meiosis most likely occurred for both parents. In other words, 'Gentle Giant' having 52 chromosomes received something similar to 26 chromosomes each from both the tetraploid 'Point Defiance' and the triploid 'Platinum Pearl'.

Rhododendron 'Gentle Giant' was also determined to be a tetraploid using flow cytometry by Dr. Thomas Ranney, J.R. Jones, and Nathan Lynch.